Iran's Islamic authorities are preparing a crackdown on women flouting the stringent dress code in the clearest sign yet of social and political repression under President Mahmoud Ahmadinejad.

From today police in Tehran will be under orders to arrest women failing to conform to the regime's definition of Islamic morals by wearing loose-fitting hijab, or headscarves, tight jackets and shortened trousers exposing skin.

Offenders could be punished with £30 fines or two months in jail. Officers will also be authorised to confront men with outlandish hairstyles and people walking pet dogs, an activity long denounced as un-Islamic by the religious rulers.

The clampdown coincides with a bill before Iran's conservative-dominated parliament proposing that fines for people with TV satellite dishes rise from £60 to more than £3,000. Millions of Iranians have illegal dishes, enabling them to watch western films and news channels.

The dress purge is led by a Tehran city councillor, Nader Shariatmaderi, a close ally of Mr Ahmadinejad who helped to plot last year's election victory.

Loosely arranged headscarves - exposing glamourous hairstyles - and shorter, tight-fitting overcoats (manteaus) became a symbol of the social freedoms that flourished under the reformist presidency of Mohammed Khatami.

During his election campaign, Mr Ahmadinejad dismissed fears that his presidency might herald a forced reversal, saying Iran had more urgent problems.

However, Mr Shariatmaderi denounced the trends as "damaging to revolutionary and Islamic principles". "We are looking for a social utopia to live in but in the last couple of months, our attention has wavered," he told fellow councillors. "In the present international situation, people must unite under known principles."

The clampdown recalls the aftermath of the 1979 Islamic revolution, when women wearing lipstick were often confronted by female vigilantes wiping their faces clean with handkerchiefs, which were said to often conceal razor blades.

The new campaign will hold taxi agencies accountable for their passengers' attire, police will be able to impound cabs carrying women dressed "inappropriately". Agencies guilty of repeat offences will be closed. Police have reportedly been stopping women motorists recently whose hijab was judged inadequate. Police have also raided fashion stores and seized brightly coloured manteaus.

Tehran's police chief, Morteza Talai, said the campaign would try to clamp down on people making "the social environment insecure".

Young women shopping in north Tehran's fashionable Tajrish neighbourhood yesterday, however, were uncowed. Matin, 24, a nurse, was wearing a gaudily patterned light-blue head scarf pushed back to reveal sunglasses and bleached blond hair. Her tight, short black manteau with intricate gold patterns seemed designed to provoke the ire of the authorities. But she was unrepentant. "I'm a married woman and it should be my husband who tells me what and what not to wear. He likes the way I dress," she said.

Surprisingly, Narges Asgari, 20, a dressmaker wearing an all-encompassing black chador, was also critical. "I don't think people will listen because they want to take decisions themselves," she said. "Clothes depend on the culture of their families. I wear the chador because, in my family, it's something we accept."